Detonating devices

ABSTRACT

A detonating device consisting of a container closed at one end and having a barrier at the other end, a secondary explosive within the container spaced by a gap from the barrier and means for ignition whereby after ignition the explosive composition is impelled against the barrier before it is completely burnt and thereby detonated.

United States Patent Dedman et al.

Apr. 10, 1973 DETONATING DEVICES Inventors: Arthur John Dedman, Nazeing;Al-

bert Leonard Lovecy, London, both of England Minister of Technology inHer Britannic Majestys Government of the Kingdom of Great Britain andNorthern Ireland, London, England Filed: Jan. 27, 1970 Appl. No.: 6,305

Assignee:

Foreign Application Priority Data Jan. 30, i969 Great Britain ..5,l83/69US. Cl. ..l02/28 R, 102/702 R Int. Cl. ..F42c 19/12 Field of Search..lO2/28, 70.2

[56] References Cited UNITED STATES PATENTS 3,088,006 4/1963 Kabik etal, .v 102/28 X 2,891,477 6/l959 Swanson ..102/28 Primary ExaminerVerlinR. Pendegrass Attorney-Stevens, Davis, Miller 8!. Mosher [5 7 ABSTRACT Adetonating device consisting of a container closed at one. end andhaving a barrier at the other end, a secondary explosive within thecontainer spaced by a gap from the barrier and means for ignitionwhereby after ignition the explosive composition is impelled against thebarrier before it is completely burnt and thereby detonated.

10 Claims, 1 Drawing Figure DETONATING DEVICES The present inventionrelates to devices which carry out the initiation of explosives.

It is known that explosives can be initiated by the direct action of ashock wave of adequate strength, as for instance the explosive wave of adetonator, or by the physical impact of a solid projectile havingsufficient mass and velocity.

It is also known that substantially most of the widely used highexplosives cannot ordinarily be caused to detonate by a directly appliedstimulus of thermal energy alone especially in those cases in which theamount of explosive is small, as for example one-tenth of a grammeand/or when the thermal stimulus is weak, for example a tenth of acalorie. The term secondaryexplosive' is normally used to distinguishthese high explosives from the class of primary explosives which readilygenerate an explosive shock wave in response to a directly appliedthermal stimulus.

In general, the established practice for the initiation of secondaryexplosives relies upon the use of primary explosives, thermallyinitiated, to produce an explosive shock to which the secondaryexplosive responds. Other methods include the use of explodingbridgewires. The correct functioning of the latter types are dependenton special control of the packing-density and other features of theexplosive used, and they cannot be used with fully consolidatedsecondary explosive.

Hitherto, the initiation of detonation of a solid secondary explosivehas been explained in terms of a physical shock-front moving rapidlythrough the explosive and a region of chemical reaction (the reactionfront) in progress behind the shock front contributing energy whichenables the shock-front eventually to achieve and maintain thoseconditions of exceptional pressure, temperature and speed which arecharacteristic of detonation. It therefore follows that all thetechniques of initiation now in use produce a detonation wave whichpasses through the secondary explosive in the same direction as theforce of impact delivered on this explosive by the explosive wave ormetal plate or other means of initiation.

In contradistinction to the known techniques of initiation, it has nowbeen found that initiation can occur by a different mechanism whicharranges for a compression wave to be produced which moves to meet theadvancing reaction-front to produce those conditions which can changethe lower rate of reaction to detonation. Initiation utilising thismechanism has been achieved by consolidating a small quantity ofsecondary explosive composition in a suitable container, closed at oneend, and placing a barrier, distanced so that there is a small gapbetween the end face of the explosive composition and the barrier, inthe path of the explosive. On ignition at or near to the closed end,gases are produced and the pressure rises in a manner dependent on theinterplay between the rate of gas production and the resistance of thevarious component parts against deformation and displacement. As aconsequence, accelerating motion of the column of explosive takes placein a direction away from the closed end and the column is projectedagainst the barrier. A compression wave originating at the collisioninterface, travels back through the explosive column to coincide withthe reaction front and produce the conditions necessary for detonation.The ensuing detonation thus travels in the opposite direction to that ofthe compression wave.

The single FIGURE of the drawing shows a crosssectional diagram of thedetonating device.

According to the invention, there is provided a detonating devicecomprising a tubular container closed at one end and having a barrier atthe other end, a secondary explosive composition within the saidcontainer spaced by a gap from the barrier, and means for igniting theexplosive composition at or near to the closed end so that afterignition the explosive composition is impelled against the barrierbefore it is completely burnt whereby the resulting impact of theremaining composition against the barrier produces a compression wave totravel back through said composition enabling it to detonate.

The explosive composition would normally be ignited at or near theclosed end of the container. Ignition may be effected by any knownmeans. For instance, it may be effected directly by electrical means orby mechanical impact energy or indirectly by contact with the reactionproducts from a different composition, hereinafter called the ignitercomposition, to which the originating stimulus is applied. The ignitercomposition may be enclosed within the container into which thesecondary explosive composition is also consolidated or may be containedin a separate component part of the device, in which case the two partsof the device must be situated substantially in contact with oneanother. I

The container may conveniently comprise a metal tube orchannel.

The secondary explosive composition may consist of any high explosivefalling within this definition, as for instance pentaerythritoltetranitrate (P.E.T.N.), cyclotrimethylene trinitram'ine (R .D .X.cyclotetramethylenetetranitramine (HMX) and nitrocellulose. The lengthof the column of this composition may be in the order of fivemillimetres or less. With such a length of explosive column, pressureswithin the device can be raised within a few micro seconds to exceed theyield strength of the metal within which the explosive is contained.

The barrier may consist of a rigid solid, a liquid barrier or a materialof consistency intermediate between a liquid and a rigid solid. In aspecific embodiment, it may consist of a substance capable of explosionand can therefore undergo detonation consequent on the detonationproduced in the column of secondary explosive which collides with it. Inall cases, the barrier must present sufficient impedance to theprojected column of secondary explosive to originate a compression waveat the collision interface which travels back through the projectedcolumn.

In one embodiment of the invention, the detonating device comprises anelectroexplosive device wherein the closed end of the container isprovided with means for igniting the explosive composition by passing anelectric current through it. The secondary explosive composition for usein the embodiment may consist in part or in whole of a mixture of asecondary explosive and conducting fibres or filaments as described incopending [1.8. application Ser. No. 7,239.

The invention is illustrated by the following examples in which thecontainer used for the explosive was a steel tube 6.3 mm. outsidediameter and 15 mm. in length with a cavity 13 mm. long closed at oneend through which passed a steel wire 22 S.W.G. securely fitted andinsulated to serve as an electrode extending internally and axially lessthan 4 mm. The cavity diameters given are nominal corresponding to thedrill sizes used.

EXAMPLE 1 The cavity in this case being 1.66 mm diameter, twomilligrammes of a mixture of PETN with carbon fibres in accordance withapplication No. 38497/66 was introduced and then a further eighteenmilligrammes of PETN alone. The successive increments were consolidatedby mechanical pressure exceeding 10,000 lbs. per square inch, then adisc of steel 1 mm thick was pressed on top. A mild steel plate 2 mmthick was placed in contact with the open end of the cavity leav ing anair-gap of 5.5 mms. between the explosive and the plate. The electricalresistance between the central electrode and the body was found to beeight ohms. The device was fired by the discharge from a condenser, lpF,at an initial voltage 300V. A hole 2.5 mm diameter was punctured throughthe steel plate in less than 25 microseconds from closing the firingswitch.

The device used in example 1 comprises a steel tube 6 closed at one end7 through which passes a steel wire 8 insulated by a suitable insulator9 from the steel end 7. The steel wire 8-extends internally and axiallyto serve as an electrode. The cavity of the tube 6 was packed with twomilligrammes of a mixture of PETN with carbon fibres 10 in accordancewith copending U. S. application, Ser. No. 7,239, and then a further 18milligrammes of PETN alone 11. A disc of steel plate 12 was placed incontact with the PETN 11 and a steel plate 14 placed in contact with theopen end of tube 6 forming an air gap 13.

EXAMPLE 2 A similar experiment in which a layer of inert powder (talc)was introduced between the explosive and the metal disc, the depth ofthe said layer being 1.5 mm after pressing. The air-gap was 4.2 mms. Theelectrical resistance was found to be 65 ohms and on firing in themanner above described, a hole 2.25 mm diameter was punctured in thesteel plate 2 mm thick.

EXAMPLE 3 The cavity in this case being 2.38 mm diameter, 8 milligrammesof the aforesaid admixture of PETN and carbon fibres was introduced,then a further 42 milligrammes of PETN alone, and finally a brass disc0.75 mm thick. The air-gap was 3.0 mms. On firing by connecting to a36-volt battery, a hole 3.5 mm diameter was punctured in the steel plate2 mm thick.

EXAMPLE 4 The cavity in this instance being 3.18 mm diameter, 15milligrammes of admixture of RDX and carbon fibres was introduced, thena further 75 milligrammes of RDX alone, and finally a steel disc 1 mmthick, the successive increments being pressed as stated above.

The air-gap was 5.2 mm. On firing from a condenser as in example 1, ahole 4 mm diameter was punctured in the steel plate 2 mm thick, in lessthan 30 microseconds after closing the firing switch.

EXAMPLE 5 A similar experiment to example 4, using HMX in place of RDXand firing by connecting to a 36-volt source of current, gave a hole 4mm diameter in the steel plate 2 mm thick. The air-gap was 5.1 mm. Theelectrical resistance before firing was ohms.

Other examples illustrating the invention are:

EXAMPLE 6 An igniter component was made comprising a steel block with acavity 2.4 mm. diameter containing 20 mg. of an intimate mixture ofantimony sulphide, 30 percent, with potassium chlorate, 70 percent,together with means of igniting the mixture electrically.

A second component comprising a steel tube 15 mm. long and 3.2 mm. bore,with mg. pentaerythritol tetranitrate (PETN) occupying 7 mm. of thelength at one end, was attached directly to the igniter componentaforesaid so that the PETN in the one and the chlorate mixture in theother were in contact and coaxial. A steel disc 1 mm. thick was pressedonto the end of the PETN column, leaving 7 mm. of the tube unoccupied. Aflat steel plate 2 mm. thick was placed over the end aperture of thetube.

On firing the igniter electrically, the 2 mm. plate was perforated witha hole 4.5 mm. diameter.

EXAMPLE 7 In a precisely similar experiment to that described in example6 the metal components were kept 0.1 mm. apart by means of a perforateddisc of paper, the explosive charges being directly in contact as inExample 6. On firing, the 2 mm. plate was not perforated, but onlybulged and cracked with the steel disc remaining embedded in it.

EXAMPLE 8 Using the same conditions as example 6, 20 mg. of silverpicrate was substituted for the chlorate mixture. On firing, the platewas perforated as before.

EXAMPLE 9 Using the same conditions as in example 6, 18 mg. of leaddinitroresorcinate was substituted for the chlorate mixture. On firing,the plate was perforated.

An assembly of two component parts as described in the above exampleswas equally successful when PETN admixed with conducting fibres'asdescribed in application No. 38497/66 took the place of the ignitercompositions above-mentioned.

The following example illustrates an embodiment of the present inventionusing a mechanical impact as the originating stimulus leading todetonation by the mechanism claimed in the present Application.

EXAMPLE 10 A steel tube 6.3 mm. outside diameter and 15 mm. long withinternal cavity 3.2 mm. diameter and 13 mm. long was fitted with a steelrod 1 mm diameter passing through a clearance aperture in the endclosure of the tube. The end of the rod inside the tube penetrated lessthan 1 mm. into a small charge of PETN, approximately mg., which was putin and consolidated with the rod already in position. The said charge ofPETN contained an admixture of gritty particles as a means of renderingthe explosive more sensitive, in accordance with general knowledge. Ametal disc next to the charge also assisted in obtaining the desiredresult. Additional PETN, in which no grit was necessary, made up thetotal of explosives to approximately 80 mg. At the end of the column wasa second metal disc and 5 mm. of the tube remained unoccupied.

The device was placed with the open end down resting on a 2 mm. steelplate supported on a steel annulus. By striking the rod projecting fromthe opposite end, the PETN charge was caused to detonate and the steelplate was punctured. Mechanical energy for striking the rod was providedby dropping a 56 gramme mass from 30 cm. height.

In the following example, it was demonstrated that water can be used asthe barrier to produce the conditions necessary for detonation and thedetonation then transmits a powerful shock wave into the water wherebyknown physical efiects such as deformation of metals may be produced.

EXAMPLE 1 1 Eight milligrammes of a mixture of PETN and carbon fibreswas introduced into a tube 6.3 mm. outside diameter and 15 mm. in lengthwith a cavity 2.38 mm. diameter, then a further 42 mg. of PETN alone andfinally a brass disc 0.75 mm. thick. This device was held verticallywith its open end downwards and dipping below the surface of water in ametal tank. The only barrier in the path of the explosive charge was thewater surface just within the open end of the tube, approximately 5 mm.distant from the end of the explosive charge. On firing, the PETN chargedetonated and the shock wave transmitted through the water deformed thetin plate base of the tank to correspond with the embossings on themetal blocks supporting it.

EXAMPLE 12 An electroexplosive device constructed in accordance withthis invention comprises a short cylinder or disc of metal supporting anelectrode which extends axially through an aperture in an end face of ahollow metal tube. The longitudinal axes of the cylinder or disc and themetal tube are substantially coincident and the two members are rigidlyconnected by a non-conducting means such as, for instance, an insulatingcement. A tubular extension from the hollow metal tube extends from theopen end of the tube remote from the apertured end face of the tube andis substantially coaxial therewith. The tubular extension isconveniently detachably attached to the hollow metal tube.

In assembling the electroexplosive device, a chosen mixture of explosiveand conducting fibres is loaded under compression into the hollow tubeto surround the electrode and make electrical contact with both theelectrode and the hollow tube. Further explosive may, if desired, byloaded into the hollow tube adjacent to the mixture. The total amount ofexplosive so loaded into the hollow tube is chosen so that a portion ofthe bore of the hollow tube is left empty at a position ad-- jacent tothe point for attachment of the tubular extension to the hollow tube.The tubular extension is loaded, before attachment to the hollow tube,with a further charge which may be of the same or different explosive,suitably consolidated and the tubular extension is then attached to thehollow tube so as to leave a minimum air gap between the charges inrespectively the tube and the tubular extension measuring at least 3 mmand preferably about 5-7 mm.

The assembled electroexplosive device is fired by applying an electricalpotential between the electrode and the hollow tube. The explosivecomponent of the mixture is ignited and there is a rapid rise in therate of explosive decomposition (transmitted through any charge adjacentto the mixture) to a speed of the order of 1,000 metres per second interms of the linear propagation of the reaction front towards thetubular extension. Products of this swift propagation or low orderdetonation then impinge upon the explosive charge in the tubularextension with a combined effect of heat and pressure sufficient toproduce a high order detonation in this explosive charge.

Electroexplosive devices of this type, when loaded with a PETN/10percent carbon fibre mixture, an adjacent charge of PETN and a PETNcharge in the tubular extension have given action times betweenapplication of firing current and detonation in the tubular extension aslow as 15 microseconds when fired by a condenser charged at about 400volts.

What we claim is:

1. A detonating device comprising a tubular container closed at one end,a secondary explosive composition adjacent said closed end, means forigniting said composition near to said closed end and thereby impellingsaid secondary explosive composition away from said closed end, andmeans for enabling said ignited secondary explosive composition todetonate comprising a barrier at the other end of said tubular containerand spaced by a gap from said secondary explosive composition, saidignited secondary explosive composition being impelled bodily before itis completely burnt against said barrier whereby the impact of theremaining secondary explosive composition against the barrier produces acompression wave which travels back through said secondary explosivecomposition to enable it to detonate.

2. A detonating device according to claim 1 wherein the barriercomprises a liquid.

3. A detonating device according to claim 1 wherein the barriercomprises a rigid solid.

4. A detonating device according to claim 1 wherein the barrier is asubstance capable of explosion which may be detonated consequent on thedetonation produced in the column of explosive in the detonating device.

5. A detonating device according to claim 1 wherein the secondaryexplosive composition is selected from a group consisting ofpentaerythritol tetranitrate, cyclotrimethylene trinitramine,cyclotetramethylene tetramine and nitrocellulose.

6. A detonating device according to claim 1 wherein the secondaryexplosive composition comprises at least in part a mixture of asecondary explosive and an electrically conducting fibre, and the meansfor ignition com-prise electrical means.

7. A detonating device according to claim 1 wherein the means forignition comprises the reaction products from an igniter composition.

8. A detonating device according to claim 7 wherein the ignitercomposition is enclosed within a separate component part of the device,said separate component part being situated substantially in contactwith the tubular container in which the secondary explosive compositionis consolidated.

9. A detonating device according to claim 1 wherein the means forignition comprise mechanical impact means.

10. A method of detonating a secondary explosive composition comprisingthe steps of a. placing said secondary explosive composition in atubular container adjacent a closed end, said container having a barrierat the other end spaced from said secondary explosive composition by a pigniting said secondary explosive composition near detonating saidsecondary explosive composition,

said detonation being produced by said compression wave travelling backthrough said secondary explosive composition when it coincides with saidreaction front moving in the opposite direction.

1. A detonating device comprising a tubular container closed at one end,a secondary explosive composition adjacent said closed end, means forigniting said composition near to said closed end and thereby impellingsaid secondary explosive composition away from said closed end, andmeans for enabling said ignited secondary explosive composition todetonate comprising a barrier at the other end of said tubular containerand spaced by a gap from said secondary explosive composition, saidignited secondary explosive composition being impelled bodily before itis completely burnt against said barrier whereby the impact of theremaining secondary explosive composition against the barrier produces acompression wave which travels back through said secondary explosivecomposition to enable it to detonate.
 2. A detonating device accordingto claim 1 wherein the barrier comprises a liquid.
 3. A detonatingdevice according to claim 1 wherein the barrier comprises a rigid solid.4. A detonating device according to claim 1 wherein the barrier is asubstance capable of explosion which may be detonated consequent on thedetonation produced in the column of explosive in the detonating device.5. A detonating device according to claim 1 wherein the secondaryexplosive composition is selected from a group consisting ofpentaerythritol tetranitrate, cyclotrimethylene trinitramine,cyclotetramethylene tetramine and nitrocellulose.
 6. A detonating deviceaccording to Claim 1 wherein the secondary explosive compositioncomprises at least in part a mixture of a secondary explosive and anelectrically conducting fibre, and the means for ignition compriseelectrical means.
 7. A detonating device according to claim 1 whereinthe means for ignition comprises the reaction products from an ignitercomposition.
 8. A detonating device according to claim 7 wherein theigniter composition is enclosed within a separate component part of thedevice, said separate component part being situated substantially incontact with the tubular container in which the secondary explosivecomposition is consolidated.
 9. A detonating device according to claim 1wherein the means for ignition comprise mechanical impact means.
 10. Amethod of detonating a secondary explosive composition comprising thesteps of a. placing said secondary explosive composition in a tubularcontainer adjacent a closed end, said container having a barrier at theother end spaced from said secondary explosive composition by a gap, b.igniting said secondary explosive composition near to said closed endthereby producing a reaction front moving toward said barrier andimpelling said secondary explosive composition bodily whilst stillburning against said barrier, the impact of the remaining secondaryexplosive composition against the barrier producing a compression wavewhich travels back through said secondary explosive composition, and c.detonating said secondary explosive composition, said detonation beingproduced by said compression wave travelling back through said secondaryexplosive composition when it coincides with said reaction front movingin the opposite direction.